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Monthly Archives: July 2010
DOCSIS 3.0 Tutorial – Downstream Channel Bonding
Downstream Channel Bonding is perhaps the ball bearings of DOCSIS 3.0, enabling subscriber data speeds in excess of 160 Mbps (4 times that of previous DOCSIS versions). While conceptually simple, the principle of combining multiple downstream DOCSIS channels together to carry the same user data must have tight constraints in order to preserve the integrity of the data and have the data arrive at the correct subscriber’s device and in sequence. This article will cover both the physical layer aspects and DOCSIS protocol aspects that enable channel bonding. Continue reading
Posted in DOCSIS 3.0
Tagged CER, channel bonding, CMTS, Codeword Error Rate, DOCSIS, DOCSIS 3.0, docsis tutorial, edge qam, eQAM, MAC, MAP, Media Access Layer, Physical Layer, QAM, Telecommunications, tutorial
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DOCSIS 3.0 Tutorial – Basic Protocol 1
Now that we have established the two primary architectures available in DOCSIS 3.0, I-CMTS and M-CMTS (thought hybrids do exist), and the hardware components of these architectures, it is time to delve into the protocol of the DOCSIS specifications that make up DOCSIS 3.0. There are five primary specifications that I will be drawing upon from here on out listed below and located in my document library and also on the CableLabs website. Continue reading
Posted in DOCSIS 3.0
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DOCSIS 3.0 Tutorial – DOCSIS Timing Interface Specification
Before DOCSIS 3.0 and before modular CMTS architectures, a CMTS existed in one chassis. Life was much simpler for everyone. Inside the chassis existed a 10.24 MHz clock or oscillator. This was a master time keeper that kept event in synchronization with every other event. Timing is very important in communications networks, especially when dealing with microsecond timing calculations necessary for DOCSIS transport – remember the “tick” (6.25 usec). This article is going to address the DOCSIS Timing Interface Specification (DTI) and DTI time servers that have arisen due to the distributed architectures in M-CMTSs and DOCSIS 3.0 CMTSs. In these architectures, it is possible to have the CMTS core in say the headend, with the eQAM and upstream receivers in remote hubsites. Suddenly the single 10.24 MHz clock keeping the system in synchronization is no longer an option. Three separate, free running 10.24 MHz clocks would also not work because they would not be in phase and would likely not be exactly running at the same frequency, causing the entire system to out of synchronization – there would packet collisions and lost data and VoIP packets all over the place. It would be chaos! So the smart folks at Cablelabs put together the DTI specification to resolve these issues. Here are some of the details. Continue reading
Posted in DOCSIS 3.0
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